1. Field of the Invention
The present invention relates to a fuel cell and specifically to a structure of a channel for taking in fuel or oxygen supplied from a manifold.
2. Description of the Related Art
A solid polymer fuel cell that uses a proton conducting polymer film for a proton exchange membrane is a power generation system in a test and development phase for commercialization, and has a problem of expensive material cost.
A separator is one of components using high-cost materials in a fuel cell. A separator refers to an electron-conductive plate including gas channel grooves for isolating two reaction gases so that they will not mix.
Since internal environment of a fuel cell is a corrosive atmosphere while the fuel cell is generating electricity, the separator is required to be highly corrosion-resistant. Besides, a separator material needs such characteristics as structural strength, gas impermeability, and low resistance.
Thus, at present, as the separator material, a dense graphite plate on which gas channels are provided or a mold graphite separator in which channels are formed in resin mold graphite made of artificial graphite particles caked with a resin is used.
Meanwhile, a metal separator using metal materials may reduce the cost. Since a metal material not only has high strength and can be thinned but also has excellent workability, the material cost and machining cost per separator can be significantly reduced.
In general, the metal material forms corrosion products under such environment where the fuel cell generates power. However, a metal separator whose corrosion resistance is improved by forming a special material on a surface or applying conductive protective paste on the surface is now being developed.
As a carbon separator has a thickness of about several millimeters or more, channels can be formed independently on a front side and a back side. However, in the case of the metal separator, a plate having a thickness of 0.5 mm or less is pressed to form gas channels thereon. As a result, concavo-convex parts of the channels are formed that are reflections of a shape of the front side of the plate on the back side.
When a separator is formed by combining a plurality of metal plates, the channel shapes on the front and the back sides are independent to each other; however, the cost is high. To form a separator in the most inexpensive manner, it is preferable to fabricate the separator by processing only a single metal plate.
In this case, since gas channels are formed by utilizing the front and the back sides of a plate in which the channels were formed, only common channel parts on the front and back sides will be formed. For example, if an introducing channel that directs gas from a manifold to an electrode surface is press-formed in a metal plate, gas from the manifold flows into the both front and back sides of one separator, which thus makes power generation impossible.
Thus, it is difficult to form a channel connecting the manifold with the electrode surface, on a metal plate.
For this reason, Japanese Patent Application Publication No. 2007-02737 discloses a separator using a metal material in which a gas channel to the electrode surface is formed by devising a configuration of materials around the manifold.
However, since the separator with a slit-shaped structure between the manifold and the electrode channel has a relatively soft material such as an electrolyte material, or a seal material arranged on its surface, the separator has a problem that the material is deformed to fit the concavo-convex parts on the surface, and thus supplied hydrogen and air are mixed in a cell. When hydrogen and air are mixed in the cell, a reaction progresses locally, thus increasing distribution of temperatures. This is one of reasons for deteriorated cell performance.
Thus, Japanese Patent Application Publication No. 2004-165043 proposes an approach using a separator substrate and two frames for forming a separator so as to prevent a gas crossover from occurring at a portion where the separator comes into contact with a proton exchange membrane.
In addition, in Japanese Patent Application Publication No. 2007-027037, the surface of the slit-like structure on which the electrolyte material or the seal material is arranged is concavo-convex shaped. By contrast, the above proposal states that a flat and smooth surface can prevent deformation of a material, and consequently, excellent sealing properties can be maintained.